The first thing I need to address was alignment of the linkage. I wasn't crazy about trying to run linkage from a servo mounted on the tray down to where I planned to mount the horn on the vent door, so I designed my own dropped & channeled servo tray out of some 1/16" plastic. I first cut the hole for the HXT 900 9g servo, and then took the hot air gun and started forming the tray. Once I got the dimensions and depth I wanted for the hole between the rudder and elevator mounts, I dropped the entire assembly down in there, and had a much better alignment for the linkage.

The door, on the other hand, was a bit more difficult. Because it fit so tight in the bay opening, I knew I would have to remove it so I could clearance it so it would swing clear and not bind the servo. To get the door out I had to cut the foam swivel hinges on the sides. I used a piece of FMS fiberglass spar material for the new hinge rod, and anchored it with two 1/2 x 1/2 square tubing plugs on both sides. I drilled the square centers of the plugs out to accept the round spar, and fit them to the side of the fuse. I epoxied one of those larger aluminum 30mm tall control horns to the door so I would have enough room for the linkage to clear the pivot spar.
NOTE:I finally got a perfect match for the Gunfighter green. I mixed 1:1 Testors MM Medium Green #FS34102 with MM Olive Drab #FS34087 and it proved to be a perfect match. When applied with an airbrush it goes on flat, so to achieve the same sheen as the factory finish, I sprayed a coat of Krylon Crystal Clear Satin over it.